[PATCH] [X86][AVX] Fix wrong lowering of v4x64 shuffles into concat_vector plus extract_subvector nodes.

[Andrea Di Biagio]

Hi Quentin,

Patch updated.
Please let me know if ok to submit.

Thanks again for your time!
-Andrea


http://reviews.llvm.org/D8259

Files:
  lib/Target/X86/X86ISelLowering.cpp
  test/CodeGen/X86/lower-vec-shuffle-bug.ll

Index: lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- lib/Target/X86/X86ISelLowering.cpp
+++ lib/Target/X86/X86ISelLowering.cpp
@@ -9021,12 +9021,12 @@
                                VT.getVectorNumElements() / 2);
   // Check for patterns which can be matched with a single insert of a 128-bit
   // subvector.
-  if (isShuffleEquivalent(V1, V2, Mask, {0, 1, 0, 1}) ||
-      isShuffleEquivalent(V1, V2, Mask, {0, 1, 4, 5})) {
+  bool OnlyUsesV1 = isShuffleEquivalent(V1, V2, Mask, {0, 1, 0, 1});
+  if (OnlyUsesV1 || isShuffleEquivalent(V1, V2, Mask, {0, 1, 4, 5})) {
     SDValue LoV = DAG.getNode(ISD::EXTRACT_SUBVECTOR, DL, SubVT, V1,
                               DAG.getIntPtrConstant(0));
     SDValue HiV = DAG.getNode(ISD::EXTRACT_SUBVECTOR, DL, SubVT,
-                              Mask[2] < 4 ? V1 : V2, DAG.getIntPtrConstant(0));
+                              OnlyUsesV1 ? V1 : V2, DAG.getIntPtrConstant(0));
     return DAG.getNode(ISD::CONCAT_VECTORS, DL, VT, LoV, HiV);
   }
   if (isShuffleEquivalent(V1, V2, Mask, {0, 1, 6, 7})) {
Index: test/CodeGen/X86/lower-vec-shuffle-bug.ll
===================================================================
--- test/CodeGen/X86/lower-vec-shuffle-bug.ll
+++ test/CodeGen/X86/lower-vec-shuffle-bug.ll
@@ -0,0 +1,41 @@
+; RUN: llc -mtriple=x86_64-unknown-unknown -mattr=+avx < %s | FileCheck %s
+
+define <4 x double> @test1(<4 x double> %A, <4 x double> %B) {
+; CHECK-LABEL: test1:
+; CHECK:       # BB#0:
+; CHECK-NEXT:    vinsertf128 $1, %xmm1, %ymm0, %ymm0
+; CHECK-NEXT:    retq
+entry:
+  %0 = shufflevector <4 x double> %A, <4 x double> %B, <4 x i32> <i32 undef, i32 1, i32 undef, i32 5>
+  ret <4 x double> %0
+}
+
+define <4 x double> @test2(<4 x double> %A, <4 x double> %B) {
+; CHECK-LABEL: test2:
+; CHECK:       # BB#0:
+; CHECK-NEXT:    vinsertf128 $1, %xmm0, %ymm0, %ymm0
+; CHECK-NEXT:    retq
+entry:
+  %0 = shufflevector <4 x double> %A, <4 x double> %B, <4 x i32> <i32 undef, i32 1, i32 undef, i32 1>
+  ret <4 x double> %0
+}
+
+define <4 x double> @test3(<4 x double> %A, <4 x double> %B) {
+; CHECK-LABEL: test3:
+; CHECK:       # BB#0:
+; CHECK-NEXT:    vinsertf128 $1, %xmm1, %ymm0, %ymm0
+; CHECK-NEXT:    retq
+entry:
+  %0 = shufflevector <4 x double> %A, <4 x double> %B, <4 x i32> <i32 0, i32 1, i32 undef, i32 5>
+  ret <4 x double> %0
+}
+
+define <4 x double> @test4(<4 x double> %A, <4 x double> %B) {
+; CHECK-LABEL: test4:
+; CHECK:       # BB#0:
+; CHECK-NEXT:    vinsertf128 $1, %xmm0, %ymm0, %ymm0
+; CHECK-NEXT:    retq
+entry:
+  %0 = shufflevector <4 x double> %A, <4 x double> %B, <4 x i32> <i32 0, i32 1, i32 undef, i32 1>
+  ret <4 x double> %0
+}

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